Correlation of crude oils



Jan. 25, 1955 J. F. BLACK ET AL 7 2,700,593 CORRELATION 0F CRUDE OILSFiled Dec. 1, 1949 3 Sheets-Sheet l FLOW DIAGRAM FOR FIQACT/ONAT/QN OFCQUDE OILS BY PRECIPITATION METHODS -50 cc. cauoa OIL 500 cc. N- PENTANEeec/ z TA TE 500 cc; N-PENTA NE I PENTANE SOLUBLE FRACT/o/v P/aE-c ZP/TA TE 500cc. Az-psAn-Aue RES ms page [PITA r5 IOQOCC.IN-=HEPTANE HEPTANESOLU L PENTA NE IN LU LE CARBCN DIS ULF/DE s ASPHALTENE V susmsavo EDSEDIMNT MM TM Z w 83 /11 mm W Jan. 25, J F. BLACK ET AL 2,700,593

CORRELATION OF CRUDE OILS Filed Dec. 1, 1949 5 Sheets-Sheet 2 RELATIVEEMISSION LINE lNTENS/T/ES OF ELEMENTS oerzcrco 5/ Mg Fe. v 211 N1 ca AZGa Mn c'r c2002 OIL A J l a c2005 O/LBJ 3 .51 Mg Fe. V Zn M Ca AI Ga MnCr C2005. 0/1. c: I l l I x 5/ My Fe .V Zn /v' Cd AI Ga Mn Cr CR UDE OILDJ I I Jan. 25, 1955 J. F. BLACK ET AL 2,70

CORRELATION OF CRUDE OILS Filed Dec. 1, 1949 3 Sheets-Sheet 3SPECTROCHEM/CAL ANALYSES OF PENTANE SOLUBLE FRACTIONS OF CRUDE OILSRELATIVE EMISSION LINE. INTENSIT/ES 4 OF ELEMENTS DETECTED 5/ Mg Fe. VZn Ni Ca AI Ga Mn Cr IUI I I1 .I

s/ 1 49 Fe'v Zn Ni Ca Al Ga'Mn Cr United States Patent 2,700,593CORRELATION or CRUDE OILS James F. Black, Roselle, N. .I., and Clara D.Smith,

Columbus, Ohio, assignors to Standard Oil Development Company, acorporation of Delaware Application December 1, 1949, Serial No. 130,4961 Claim. C1. 23-430) This invention relates to an improved method fordetermining similarities, or dissimilarities between crude oils. Inother words the process of this invention is of application in thecharacterization or correlation of crude oils. In accordance with thisinvention, crude oil samples are treated so as to segregate certainparticular fractions which may then be subjected to infrared analysistests, spectrochemical tests, or X-ray diffraction tests to uniquelycharacterize the crude oil samples from which the fractions weresegregated.

In oil exploration activities it is frequently desirable to determinewhether or not two oil wells are producing from the same source. Toaccomplish this it is necessary to characterize the crude oil obtainedfrom the wells. It has been the general practice to work towards thisend by determining fundamental inspections of the oils; for example, bydetermining the A. P. I. gravities, the carbon to hydrogen ratio, thedistillationcharacteristics of the oils to be compared, etc. Suchtechniques are subject to several disadvantages. For one thing it is notpossible to obtain information of this type from samples of the oilobtained by core sampling techniques. More fundamentally, methods basedon the inspections of crude oils are not sutficiently basic to establishgeological relationships between crude oils. This is true for the reasonthat the crude oil characteristics measured in these inspection testsare markedly affected by incidental and uncontrollable factors existentat a particular locale, such as the gas pressure on the producinghorizon; loss of light ends from the crude, etc.

Attempts have been made to more precisely correlate crude oils so as todetermine geological relationships between crudes by subjecting totalcrude oil samples to spectrographic and optical methods of analysis. Insome cases it is possible to successfully characterize crudes by thismethod. For example, it has been found possible to successfullycorrelate total crude oil samples by the specialized radiationabsorption technique disclosed in U. S. application Ser. No. 109,441,filed by Clara D. Smith on August 10, 1949. However, even in this casereliability of correlations established by this method are somewhatdoubtful. The method is not applicable to correlations based on coresamples and the method is subject to errors caused by loss of light endsfrom the crude, deasphalting of the crude which may have occurred in theground, and other factors.

It'is, therefore, the principal object of this invention to provide animproved technique for characterizing crude oils overcoming thedisadvantages of the methods heretofore employed, of the natureindicated above.

As indicated by the preceding description, a difliculty of existingcrude oil correlation methods relates to the variations in crude oilscaused by conditions existing in the oil trap from which the crude oilis drawn. For example, a total crude oil sample withdrawn from one wellascompared to the sample withdrawn from a diiferent well, both fed bythe same source and having the same geological history, may differ insediment content; asphalt content; light hydrocarbon content, etc. Suchdifferences can arise due to a number of factors such as the penetrationof salt water to the producing horizon, deasphalting of oil due to lighthydrocarbons present, or differences in pressure existing at theparticular point from which the crude oil is taken. Consequently, it isthe novel concept of this invention to overcome the effect of factors ofthis nature by subjecting the crude oil sample to be characterized to aparticular segregation process so as to gating reproducible fractionsfor analysis 2,700,593 Patented Jan. 25, 1955 content, etc.

In accordance with this mvention, a crude oil to be characterized issegregated into at least two fractions.

One fraction is a light hydrocarbon soluble fraction, while the secondfraction constitutes an asphaltene fraction. The method by which thesefractions are obtained is an important feature'of this inventiondepending upon particular dilution, filtration, and washing techniques.As will be disclosed, by following the segregation process of thisinvention, a light hydrocarbon soluble fraction and an asphaltenefraction will be obtained which can be examined by conventionalanalytical methods so as to indicite geological relationships betweencrude oils being teste The method of this invention may be fullyunderstood by reference to the following detailed description inconnection with the accompanying drawings in which:

Figure 1 represents a flow diagram showing a specific segregationprocess embodying this invention, which is suitable for obtainingreproducible fractions of a crude oil to be analyzed, and;

Figure 2 represents the spectrochemical analysis of the deasphaltedfractions of three distinctive crude oils obtained by the process ofthis invention, and;

Figure 3 similarly represents the spectrochemical analysis of fractionsfrom two geologically related crude oils.

Referring now to Figure 1, a specific manner of segreis represented. Asshown by this figure, a sample of crude oil is first subjected to abouta 10 to 1 dilution with a light hydrocarbon. It is presently preferredto utilize normal pentane as the dilution agent although the principlesof this invention may be adapted to the utilization of normal butane,normal propane and other C3 to C7 paratfinic hydrocarbons. Similarly,the particular extent of dilution is not particularly critical. Theaddition of normal pentane, or other light normal paraflinic hydrocarbonis effective in precipitating substantially all asphaltenes from thecrude oil. This asphaltene precipitate is then washed on a filter, forexample, with normal pentane. In the specific case illustrated in Figure1, when 50 ccs. of crude oil is diluted with 500 ccs. of normal pentaneto secure the precipitation of asphaltenes, it is suitable to wash theasphaltene precipitate with an additional 500 ccs. of normal pentane.These steps will yield a washed precipitate containing substantially allof the asphaltenes originally present in the crude oil, and will yield apentane soluble fraction of the crude oil substantially constitutingdeasphalted crude oil from which sediment has been removed by thefiltration step. As will be brought out, the pentane soluble fractionconstitutes a fraction of the crude oil which may successfully becharacterized by methods such as infrared absorptive analysis, orspectrochemical analysis so as to effectively characterize the crudeoil.

Returning now to the washed precipitate obtained as indicated bydilution of the oil with normal pentane followed by washing with normalpentane, it is necessary to subject this precipitate to further treatingsteps in order to obtain a reproducible asphaltene fraction. Thenecessity for further processing of the asphaltene precipitate arisesfrom the fact that the nature, and extent of asphaltene precipitationfrom the crude oil depends in part upon sediment present in the crudeoil, and the specific hydrocarbon composition of the oil. Thus theasphaltene precipitate as heretofore obtained is not a reproduciblefraction of the crude oil. For this reason this precipitate ispreferably subjected to a further wash with, for example, 500 ccs. ofnormal pentane. This wash is effective in dissolving a portion of theprecipitate to yield a second pentane soluble fraction, includingcertain resins originally present in the crude oil. The asphalteneprecipitate is then subjected to a wash with a hydrocarbon capable ofdissolving a portion of the asphaltenes, and other materials stillpresent in the asphaltene fraction. In other words, an agent is employedwhich is suitable to cause some of the asphaltenes present in thefraction to go back into solution. To achieve this, a paraffinichydrocarbon may be used having a greater number of carbon atoms than thehydrocarbon formerly used to precipitate the asphaltenes. For example,in the particular process being described, it is suitable to employabout 1000 ccs. of normal heptane, yielding a heptane-soluble,pentane-insoluble fraction consisting as indicated of a portion of theasphaltenes originally present in asphaltene fraction is then dissolvedin a solvent such as carbon disulfide capable of dissolving allremaining asphaltenes, but leaving any sediment present in the crude oilundissolved. A variety of asphaltene solvents may be employed such aspyridine, benzene, toluene, carbon tetrachloride, and carbon disulfide.Consequently, by filtering the solution of the asphaltenes, suspendedsediment can be removed. As will be brought out, the asphaltene fractiondissolved in a solvent such as carbon disulfide as precipitated, washedand partially redissolved, as described, will constitute a reproducibleasphaltene fraction of the original crude oil which may successfully becharacterized by conventional analytical procedures such as X-raydiffraction and infrared absorptive analysis.

As heretofore described, the novel crude oil characterization method ofthis invention depends upon the segregation of a crude oil sample intoparticular fractions. In particular, it is necessary to precipitate allasphaltenes present in an initial step to obtain a deasphalted fractionof the crude oil, and it is then necessary to particularly treat theasphaltene precipitate to obtain a reproducible asphaltene fraction ofthe original crude oil. In essence, the necessary segregation processdepends upon the initial precipitation of substantially all asphaltenes,followed by the partial solution of a portion of the asphaltenes. Bythis technique it is possible to eliminate the effect of the originalcrude oil composition on the fraction of precipitated asphaltenesobtained, and essentially the technique permits obtaining an asphaltenefraction precipitated from a control medium so as to be of areproducible nature.

In order to demonstrate the utility of the segregation process describedfor successfully characterizing crude oils, examples will be givenshowing the manner in which the crude oil fractions may be analyzed.Attention will first be directed to the methods by which the pentanesoluble fraction may be examined.

Two methods in particular are suitable for characterizing the pentanesoluble fraction. These methods are spectrochemical analysis, andinfrared spectrometry. Insofar as both of these analysis methods arewell known to the art, no description will be given of the manner inwhich they are conducted. In the case in which spectrochemical analysisis used the pentane soluble fraction is reduced to an ash which is thenanalyzed by the methods of spectrochemical analysis to provide thecomparative emission line intensities of metallic elements present inthe ash. Referring to Figure 2, typical spectrochemical analyses ofpentane soluble fractions of three crude oils are indicated, showing theresults obtained on three different crude oils. It will be noted thatthe emission line intensities of crude oils A, B and C, differ widely incharacter. Thus, for example, the fraction of crude oil B unlike thefractions of crude oils A and C does not contain vanadium, zinc,gallium, manganese, and chromium. Again, the fraction of crude oil Cunlike those of crude oil A and crude oil B contains no magnesium. Asignificant point in regard to the spectrochemical analyses indicated inFigure 2 is that no sodium is present in any of the fractions, whilesodium was present in the original crudes from which the fractions wereobtained. The absence of sodium from the pentane soluble fractiondemonstrates that the filtration step is effective in removing suspendedcontaminants. Inasmuch as the three crude oils from which samples weretaken in preparing Figure 2, 'ere selected from different geographicregions, the data of Figure 2 demonstrates that spectrochemical analysisof the ash from the pentane soluble fraction of crude oils is asensitive method for comparing crude oils.

Referring now to Figure 3, the spectrochemical analysis of the ashobtained from the pentane soluble fraction of two crude oils chosen fromthe same geographical location is represented. it will be observed thatthe emission line intensities for the two crude oils D and E are verysimilar in nature. This bears out the probability that the two crudeoils have a close geological relationship since both of the oils wereobtained from neighboring wells at Lower Cretaceous producing horizons.

As indicated by the data presented in Figures 2 and 3, therefore,spectrochemical analysis of the pentane soluble fraction of crude oilsprovides a suitable manner of characterizing crude oils so as toestablish, or disprove geological relationships between the oils.

It may be noted that attempts to obtain similar correlations byconducting a spectrochemical analysis of the total crude oils Withoutsegregation, or fractionation, was unsuccessful in providing comparativedata of the nature indicated in Figures 2 and 3.

In the event the pentane soluble fraction of crude oil is subjected toinfrared analysis procedures, similar correlations can be establishedbetween crude oils from which the pentane soluble fractions areobtained.

Referring now to the examination of the asphaltene fraction derivedaccording to the procedure indicated in Figure 1, this fraction may alsobe examined by a number of methods. A particularly effective manner isto determine the infrared absorption spectra of the asphaltene fraction.The absorption spectra may be obtained according to conventionalinfrared procedures. Table I indicates typical data obtained from theinfrared spectra of the asphaltene fraction of a variety of crude oils.Oils A through F are Canadian crude oils, while oils G through I areEgyptian crude oils. Table I indicates the relative intensity of theprincipal absorption maxima for the asphaltene fraction of these oils.

TABLE I Data from infrared spectra of asphaltene fraction from crudeoils Frequency of Bend Group C ausing Band G-H (2) Aromatic OHM-CH3 CCH;

Asphaltenes from:

Crude Oil A 2 11 31 11 Crude Oil B 100 3 12 33 11 Crude Oil C 100 2 1133 10 Crude Oil #1 D 100 8 21 35 10 Crude 100 3 16 34 10 Crude 100 2 1832 I0 Crude Oil G- 100 5 21 34 11 Crude Oil H 100 1 16 31 10 Crude OilI- 100 2 16 33 10 Crude Oil J 100 4 17 34 9 (1) Base line densities fromeach spectrum were multiplied by a factor which would convert thedensity of the 3400 cm.- absorption band to avalue of 100.

(2) Possibly C=O.

Referring to the Canadian oils (oils A-F), it will be noted that withrespect to the 1700 cm." and 1615 cm." maxima, the asphaltenes from oilsA, B and C are identical within the experimental accuracy of theintensity measurements. On this same basis oil D is markedly differentfrom oils A, B and C, and finally oils E and F fall between these twoextremes. These data are in accordance with spectrochemical analyses ofthe ash content of pentane soluble fractions obtained from these oilsandbears out the supposed similarity and dissimilarity of geologicalrelationships between the oils. In considering the data relative to theEgyptian crude oils chosen from the Gulf of Suez area; that is, oils Gthrough I, it will be noted that relatively small variations exist amongthese samples. This result would be expected as the Egyptian oils arebelieved to be very similar in nature.

Similar infrared absorption comparisons may be made in other regions ofthe infrared spectra. Thus, while the data of Table I was obtained inthe 2.0 to 7.5 micron region of the spectra, if desired similar data maybe obtained bearing out these same relationships between the oils in the7 .5 to 15.0 micron infrared region.

If desired, the asphaltene fraction may also be examined by X-raydiffraction methods. Apparently crystalline material is present in theasphaltenes from all crude oils other than embronic oils which may betoo young to have formed crystalline material. Consequently, distinctiveX-ray diffraction patterns may be obtained by examining the asphaltenesby conventional X-ray techniques. Referring to typical data obtained byX-ray diffraction methods, it was found that oils chosen from theDevonian belt in Canada are clearly distinguishable from oils found inthe Cretaceous belt in Canada. Oils from the Devonian belt arecharacterized by the presence of two sharp lines in their X-rayditfraction patterns which are completely absent from the patterns ofoils of the Cretaceous belt.

As described, therefore, the present invention comprises a novel methodof characterizing crude oils. In accordance with this method a totalcrude oil sample is fractionated so as to obtain a deasphalted fractionand an asphaltene fraction. As implied, in the preceding description,all steps may be carried out at existing temperatures and pressurealthough elevated temperatures and pressures may be used if desired. Bysuitable analysis of either, or both of these fractions it is thenpossible to uniquely characterize the crude oils from which thefractions were obtained, and to establish any geological relations whichmay exist between the crude oils.

What is claimed is:

In the correlation of crude oils for the purpose of comparing crude oilsfrom different sources the steps which comprise diluting said crude oilwith a C3 to Ca paraifinic hydrocarbon whereby an asphaltene fraction isprecipitated and a light hydrocarbon soluble fraction is obtained,thereafter partially dissolving said asphaltene fraction by the additionthereto of a light parafiinic hydrocarbon having a greater number ofcarbon atoms than in the preceding step, dissolving all the remainingasphaltene fraction and separating this dissolved fraction from sedi'ment and thereafter subjecting said dissolved asphaltene fraction toexamination by radiant energy to determine the transmissioncharacteristics of said dissolved asphaltene fraction.

References Cited in the file of this patent UNITED STATES PATENTS1,868,211 Le Nobel July 19, 1932 2,143,882 Keith, Jr., et al. Jan. 17,1939 2,158,980 Brundin May 16, 1939 2,213,138 Hayward Aug. 27, 19402,257,170 Howell Sept. 30, 1941 2,300,119 Holmes Oct. 27, 1942 2,349,366Moon May 23, 1944 2,366,657 Sorem Jan. 2, 1945 2,383,535 Dickinson Aug.28, 1945 2,394,703 Lipson Feb. 12, 1946 2,462,270 Lipson Feb. 22, 19492,483,500 Long Oct. 4, 1949 2,500,757 Kiersted, Jr. Mar. 14, 1950 OTHERREFERENCES Abraham: Asphalts and Allied Substances, 4th edition, p.1008. Published by D. Van Nostrand and Co. Inc., New York, N. Y., 1938.Copy in Div. 31.

Spectrographic Analysis, by A. C. Rice et al., pages 21 and 22, 88-14 S.E.

